let p1 = new Promise((resolve, reject) => {
  resolve(11);
})

let p2 = new Promise((resolve, reject) => {
  resolve(22);
})

let p3 = new Promise((resolve, reject) => {
  resolve(33);
})

// p.then().then().then()....

// 特点：前一个then返回Promise对象，Promise对象中的结果，会被下一个then得到

p1.then(res => {
  console.log(res); // 11
  return p2;
}).then(res => {
  console.log(res); // 22
  return p3;
}).then(res => {
  console.log(res); // 33
})